(1) Field of the Invention
The present invention relates to an optical modulator module that includes light source and optical modulation device in the same package, and particularly to an optical modulator module that has the semiconductor laser as a light source.
(2) Related Art Statement
In the field of advanced optical communication, the distributed feed back semiconductor laser (DFB laser) that have stable wavelength with narrow spectrum width are commonly used as light source and generates continuous wave (CW) and the laser beam is modulated responding transmission data by the optical modulator, which is placed in external side of the semiconductor laser and the modulated light is sent by the transmission line such as optical fiber.
Moreover, the optical modulator, in most cases has the light guides on the surface of the chip made of the material of electro-optical effect, such as LiNbO3 (LN hereinafter), and electrodes near the light guides that high-speed modulate light guided in said light guides.
In such device, that produces the modulated radiation, it is general to construct the device by mutually connecting individual parts as semiconductor laser and optical modulator etc., and optical components as lens and optical fiber etc. However, according to the recently speed-up and high-capacity of data transmission for wavelength multiplex of optical networking and so on, the construction of device is becoming huge and complex and so it is increasingly needed to integrate and minimize the main components.
Furthermore, when adopting semiconductor laser as a light source, in order to stabilize the oscillation of laser beam the control of the temperature of semiconductor laser and the removal of harmful returning light to the semiconductor laser are required.
In addition, the output laser from semiconductor laser has a plane of polarization. On the other hand, for the effectively modulating operation in external modulator such as LN optical modulator, the light transiting within the modulator is needed to setup to the optimum plane of polarization in optical modulators waveguides. Therefore, it is necessary to adjust the conformity of both planes of polarization.
In case that semiconductor laser and optical modulation device as external modulator, which are main components in the transmitting sides, are integrated into the same package, the following problems need to be solved in addition to the above ones.
First of all, sometimes, the main polarized direction of the polarization plane of output laser of semiconductor laser is different from optimum polarized direction of incident light, which forms the optimum plane of polarization in LN optical modulator's waveguides. Therefore, spinning function of polarization is necessary for adjusting both of them.
Secondly, in order to control the temperature of semiconductor laser, the temperature-controlling tool such as Peltier device is mounted inside the supporting member of semiconductor laser. The effect of temperature change from said temperature-controlling tool and semiconductor laser spread to whole supporting member and cause the dimensional change of itself. Therefore, the shift of light axis will cause between the optical component, as semiconductor laser, supported by said supporting member and optical modulation device and so on set outside of the said supporting member. As a result, the increase of coupling loss, or the change of the coupling loss will occur, which disables to modulate light effectively and stably.
Moreover, waveguide mode of LN optical modulation device is small in mode diameter and it is generally asymmetric. Therefore, tolerance of alignment is very small; particularly there is a problem that the tolerance of alignment, which is vertical to the surface of package and so supporting the LN optical modulation device, is much smaller.
For this reason, when two devices, which are placed in different supporting members, are optically integrated by interval optical system, it is necessary to compose the optical integrate system, which can be placed precisely to each element and even if size change of each supporting member occurred, it has to be stable without sift of optic axis.
The objects of the present inventions are to solve the above stated problems and minimize whole device, especially offer optical modulator module with fulfilling the effective and the stable optical modulation, which stabilizes the emission of semiconductor and control the shift of optic axis between the optical component by the temperature change and so on, when using the semiconductor laser.